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Old 05-20-2000, 07:35 PM   #1
edekker
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Post Front and Rear O2 Sensors - Observations

Note:
1) My comments are about the O2 sensors found on the MY99 2.5RS. The front O2 sensor found on the MY00 do not output a signal in the typical 0.0V-1.0V range. I'm not sure about the MY98.
2) My car is mostly stock except for the Rimmer s/c (7 lbs boost) and a rising-rate fuel pressure regulator.

First - a recap, and update:
For the longest time, I've had my A/F meter conected to the rear O2 sensor. During that time the front O2 sensor had been 'lazy' and unresponsive - I couldn't get a reading that made sense. However the ECU did not throw a code until recently (about 5 weeks ago) - confirming the bad front O2 sensor.
A new one had been ordered, and installed. I've had my A/F meter connected to the new front O2 sensor for a few weeks already.

Some observations:
1) There is an interesting distinctive difference in response between the two sensors.
The front's transitional response, including its dance around the stoich, is much more quick compared to the rear. It also has a more rapid transient response - for example, throttle tip-in on deceleration causes it to go rich in a flick. The rear O2 sensor reads slower, with a seeming phase lag.

I found that very interesting. I wonder if this is how the ECU can tell about the status of the cats, and whether the cats are even there at all. If true, I think there is a way to fool the ECU - preventing that anoying CE light from coming on when a mod to the cats are made.

2) On WOT, the front shows 0.7V, never higher. The rear, however, shows a 0.8V reading consistently.

This goes against what I've been hearing (and reading) - that an A/F meter connected to the rear O2 sensor will show a reading less rich than it really is. That bothers me. It looks like I may not be running as rich as I had hoped for. I wonder if that is why I'm detting on WOT.

3) As the engine approaches 4500 RPM, the front O2 sensor switches to a consistent, and steady, 0.5V (or so) reading - no fluctuations at all. It remains in that state as long as the revs are higher than 4500 RPM. It occurs in any gear and on the lightest of loads (thottle light, manifold vacuum still high).

I think this confirms my suspicion that the ECU switches into open-loop mode at high RPMs and probably relies solely on fuel and ignition maps. It could also support Shiv's belief that the ECU ignores the knock sensor as well - I'm not sure.

Anyway, food for thought.
Ed.
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Old 05-20-2000, 09:23 PM   #2
8Complex

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Post

Just curious and I'm by far not an expert on the topic of readings and guages, but wouldn't an EGT sensor and guage be the best to tell if you're running too hot and detonating?
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Old 05-20-2000, 11:20 PM   #3
edekker
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Post

8Complex,

Having an EGT gauge is certainly a good idea. I already have one on order (an Omori - ETA mid June). But the gauge doesn't necessarily tell if det is occuring, per se. It can only tell what the temps are. If the temps are high enough - well it certainly would be one factor encouraging detonation.

I can actually hear the detonation when it occurs. What worries me is that I'm not running as rich on WOT as I had previously thought. Regardless of whether my EGTs are too high or not, I need more fuel. My RR FPR apparently is not enough, it seems. I may need a bigger FP or a fuel computer (AFC, SFC, or whatever they call it). I hope I don't need bigger injectors - that might open up another Pandora's Box (scared). I'd rather back off on the boost instead. Once I get all the gauges installed (FP, EGT and boost), hopfully I'll get some clues for an answer.

I've read that by going to a free flowing exhaust, boost pressure actually drops somewhat since the motor breaths better, yet it makes more horsepower (assuming there is more fuel to accomadate it). Can anyone tell me if this true (Shiv?)? I wonder, could that also help reduce the chance of detonation?

Much appreciated.
Ed.
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Old 05-21-2000, 08:38 AM   #4
tulit
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If you're running 7lbs of boost, thats probably why you're detting. A FPR probably isnt adequet. At the very least I would recommend you put a AFC on.
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Old 05-21-2000, 08:46 AM   #5
mjos
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Actually a SAFC will not help out. Your stock fuel pump is maxed out at the higher FP from your regulator. Install a Holley High flow pump(for the Acura). It is a perfect fit with no mods necessary. You will now have more fuel than you know what to do with at 7-14psi...ask me how I know

Mark
99' RSt
 
Old 05-21-2000, 11:21 AM   #6
edekker
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Post

Thanks for the feedback guys.

I admit I'm probably pushing my luck - running 7 lbs with no I/C, etc. But I'm almost there. I get the feeling not much more is needed to get rid of this detting problem.

The performance at 7 lbs boost is fantastic. I'd hate to lower the boost level. I hope your right - that a bigger fuel pump is all that's needed. If that were true, I would surmize the FP gauge (once installed) should show a pressure drop on WOT (on the stock pump). Please correct me if I'm wrong about that.

That would be amazing if that's all it is. With more fuel, I'd probably make more power. And, without having the burden of worrying about maxing out on WOT - I would fly!

Ed.
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Old 05-21-2000, 08:32 PM   #7
Patrick Olsen
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Post

In reply to a couple of your questions, Ed:

If air can get through the engine easier, you will see less boost. Basically, boost is the air stacking up in the intake because it has nowhere else to go. Well, if you make the engine flow air better, the air won't stack up in the intake as bad, so you'll see lower boost. That might seem like a bad thing (less boost = less power, right?), but since an engine wants air, and now the blower is able to supply it more freely, you will make more power.

Will more flow make it less likely to detonate? I would say it's just the opposite. Now you have a car that is making more power/flowing more air and you haven't fixed the lack of fuel. I think your detonation problem would be exacerbated. (ooooo, vocabulary! )

As for fuel pressure - since you have a RR FPR, you should see fuel pressure rise as boost rises - simple as that. Fuel pressure might not necessarily drop at WOT, but if it doesn't rise at the same rate boost does, then you have a problem. So if fuel pressure is rising as you climb in RPMS at WOT, and then it starts to level off or even drop, you're not supplying enough fuel.

Pat Olsen
'99 Legacy 2.5GT sedan, '89 blown & intercooled Mustang GT convertible
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Old 05-21-2000, 11:25 PM   #8
pilotdoc
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Ed, I was wondering, how accurate is your a/f meter. When it reads 0.8, could it be 0.81 or 0.89 or even less than that? If so, the sensors could be changing more than you can see, (eg with a Jumptronix meter). Sometimes an AFC is used to change a reading very slightly, from 0.82 to 0.87 for example, but changing the fuel by less than 5%.

OTOH, I was looking at Autometer's site, and they show that with increasing temperature, the O2 sensor's reading is decreased in rich conditions, so I don't know if one could consistently go for a specific reading.

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Old 05-22-2000, 07:34 AM   #9
edekker
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Post

Pat,
Thanks for the info.
I'm kind'a disheatened to hear that det is more likely with a free flowing exhaust.
And it's important for me to hear the det clearly - a free flowing exhuast usually sounds very loud, possibly drowning out any det sounds. It looks like I'm going to have to try some kind of homemade det meter first, before an exhaust is put on.

pilotdoc,
I hear what you're saying - Well... I don't put too much credence on the A/F mter. I would view any reading, especially one with a supposed accuracy to the hundredth of a volt, with a grain of salt. The O2 sensor is sensitive to temperature, which affects the reading outside of the stoic. The A/F meter reading should be interpreted more as a guide, not as an exact measurement of the A/F ratio. At a resolution of 0.1V, my meter is plenty acurate enough for me - in my opinion of course. I need to rely on other gauges such as the EGT, FP and boost to help complete the picture.

Thanks again guys,
Ed.
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Old 05-22-2000, 11:54 AM   #10
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Post

Quote:
As the engine approaches 4500 RPM, the front O2 sensor switches to a consistent, and steady, 0.5V (or so) reading - no fluctuations at all. It remains in that state as long as the revs are higher than 4500 RPM.
I'll keep this short and sweet.

And you wonder why you are detonating?
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Old 05-22-2000, 01:48 PM   #11
edekker
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Post

SteveS,

During that test, as I had indicated in my post, my throttle was very light – manifold vacuum still high. I get no detonation whatsoever during this test and that 0.5V reading can be made to occur. I don't get that 0.5V reading when the throttle is heavy. As soon as I go heavy on the throttle my reading goes to 0.7V in a flick.

In that test, as soon as I let the revs drift below 4500 RPM, the A/F reading reverts to the familiar playful dance around the stoic. As soon as I edge it back up through 4500 RPM, the reading goes to a steady 0.5V. The only thing that I had changed was the raising and lowering of the revs. It happens even in 1st – the throttle is barely on. I'm almost positive the ECU goes open loop and runs a map when the revs are higher than 4500 RPM – and chances are the ECU also ignores the knock sensor as well.

Ed.
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Old 05-23-2000, 07:33 AM   #12
SteveS
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edekker ~~ OK, point taken. But you're still overlooking the facts. 0.7v at WOT is not high enough. That's a period at the end. There's really nothing left to say, unless your O2 sensor is going bad or your meter is slightly off.

You've already had a problem with cylinder 3. I would think you would see what's plainly staring you in the face. The fuel pressure riser is NOT enough. Forget what Rimmer has told you. Do what is right. Buy the Field SFC or the Apex'i AFC and be surprised what a little fuel management can do.

If you can clearly hear detonation, your A/F meter readings are this low, and you've already busted #3, what are you waiting for? All the signs are there of running lean, lean, lean.
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Old 05-23-2000, 08:05 AM   #13
edekker
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SteveS,

I totally agree with you.

I'm waiting for my EGT gauge to arrive (ETA mid June). I've already got the boost and fuel pressure gauge but they're not installed yet. They'll all be installed once I get the EGT gauge (to save me money on the labor, I don't have tools or a garage available). I need these gauges before I can make any educated decisions on my next course of action.

What am I waing for? Well all this costing money. To accumulate the funds takes time, and the budget is tight. I've had my motor rebulit - that had drained my funds alot. I still had to take care of the tires (got a new set of BFG g-Force KDW). The ACT 'street clutch' and lightened flywheel needs to be put on this summer as well. Add to that a bigger FP (or SFC or whatever solution to my fuel requirements are), high-flo exhaust, etc. Well...I hope you see what I mean.

Ed.
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Old 05-23-2000, 08:10 AM   #14
mjos
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Man..I would invest in an EGT probe and gauge right away. Carparts.com had the autometer EGT kit with the Ultralight silver face for $85 for the entire thing...I was pissed after paying $130 from JEGS for mine.

My A/F ratio meter always showed rich under WOT with my stock FPR. When I added the EGT, I was shocked to see how inaccurate the A/F meter is since my EGT's were rising above 1600F..not good. A/F meter still showed full rich. These cars seem to run real lean under mid accell. My EGT's are around 1550 under mild boost normal driving. When I floor it, my egts are actually going down now.

Get the EGT gauge and use the A/F gauge as pretty lights

Mark
99' RSt
 
 

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